I removed and installed the plugins again and it works now.
Don't know what happened there.

If mozilla (firebird, whatever flavor) is doing anything - it won't
load new plugins until all process have finished (IE it's running) -
then it will load them next time it starts.

IE if you had a download window open or something - the new plugins
wouldn't be registered until ALL mozilla windows were closed and the
browser started fresh.

That's not entirely true. It looks for new plugins every time it is
asked to check the available plugins. That does happen at startup.
It also happens whenever you view about:plugins, or otherwise initiate
a call to navigator.plugins.refresh()